The invention relates to an energy storage module for a device for supplying voltage, particularly of a motor vehicle, comprising a plurality of prismatic storage cells which, stacked in at least one row, are arranged behind one another and braced between at least two end plates by means of at least one tie rod or a wrapping. The invention further relates to a method of producing an energy storage module.
In a device for supplying voltage to a motor vehicle usually called a battery, a plurality of energy storage modules is mostly used for the drive of the vehicle, for example, of electric vehicles or hybrid vehicles. A respective energy storage module typically consists of several stacked prismatic storage cells. The individual storage cells contain electrochemical cells of the battery. The stack of individual storage cells is usually braced by means of a mechanical end plate and tie rods to form the energy storage module. In addition to mechanically fixing the modules with respect to one another, the end plates and tie rods especially have the purpose of counteracting a deformation by the change or increase of the internal gas pressure during the operation of the electrochemical cells of the storage module arranged in the interior of the modules.
The end plates and tie rods of the conventional energy storage modules are usually produced by means of the extrusion process from steel or aluminum. The production of such so-called extruded sections is connected in this case with high production-related expenditure and the resulting high costs. Extruded sections for energy storage modules can therefore not be cost-effectively produced on a large scale. Conventional extruded sections for energy storage modules further have the disadvantage that they are heavy because of the material properties of the used material, which has a disadvantageous effect on the total weight of the motor vehicle. Furthermore, the materials forming the extruded section, such as steel or aluminum, are electrically conductive, so that an insulating layer is required between the individual storage cells and the tensioning device, in order to prevent electric couplings between the storage cells. The providing of such insulating layers is costly and increases the manufacturing expenditures of the energy storage module and thereby the costs for its production.
It is an object of the present invention to provide a cost-effective energy storage module for a device for supplying voltage, which can be produced in a simple manner and, in addition to a very high stability, has a low net weight. It is a further object of the present invention to provide a method of producing an energy storage module that requires low production-related expenditures and, in addition, permits a simple and cost-effective manufacturing of the energy storage module.
The object is achieved by means of the combinations of characteristics of the independent claims. The dependent claims indicate advantageous embodiments of the invention.
The object is therefore achieved by an energy storage module for a device for supplying voltage, particularly of a motor vehicle, comprising a plurality of prismatic storage cells which, stacked in at least one row, are arranged behind one another and braced between at least two end plates (also called pressure plates) by means of at least one tie rod or a wrapping. At least one of the end plates has a layer structure of at least three layers, and/or the tie rod consists of a composite-fiber material. Usually, one end plate respectively is mounted on the respective face side of the stacked cells disposed at the end, so that the energy storage module comprises two end plates. However, one end plate may also consist of several individual plates, in which case then, according to the invention, at least one of these individual plates has a layer structure of at least three layers and/or the tie rod consists of a fiber composite material.
If the end plate of the energy storage module according to the invention has a layer structure, this layer structure comprises at least three layers, whereby a sufficient stability of the end plate is ensured with respect to a compression deformation. Additional layers may be provided. The layers may be formed of different materials which comprise metals or alloys, such as steel and also synthetic materials, in which case the respective layers may all or partly be made of the same material or in each case of different materials. Suitable materials can be combined with one another, possibly with the aid of fastening elements or adhesive components. In comparison to conventional extruded sections, such a layer structure has the advantage that the stability of the end plates can be adjusted in a targeted manner corresponding to the demands, and furthermore, an effective weight reduction of the net weight of the end plate and therefore of the energy storage module is achieved. The production expenditures of such an end plate are also low, which lowers not only the technical and business-economics-related demands on the production of the energy storage module according to the invention but also its production costs, and thereby the costs of the energy storage module. In the case of a provided layer structure of the energy storage module according to the invention, the bracing may also take place by way of conventional tension elements, which are particularly designed in the form of tie rods.
The end plates of the energy storage module according to the invention may be braced by way of at least one tension element, particularly a tie rod or a wrapping. The number and shape of the tension elements depends on their individual design. Depending on the required stability, one tie rod or, for example, several tie rods may be provided which connect (brace) the end plates to one another which are mounted on the face side on the exterior storage cells. In this case, such a tie rod may be made of metal, for example, of steel or aluminum, and has a shape that permits a permanent connection and bracing of the storage cell module comprising storage cells and end plates.
According to the invention, the tension element is constructed as a tie rod; however, advantageously, the tie rod may also be formed of a fiber composite material. This is particularly so when conventional materials comprising extruded sections are used as an end plate. Fiber composite materials are known from the prior art. As a rule, they comprise a matrix material and corresponding fibers, the fibers being present in the matrix material in a predominantly homogenously distributed fashion, which contributes significantly to the stability of the fiber composite material. Because the net weight of the fiber composite material is lower than that of conventional metallic materials, the use of a tie rod made of fiber composite material reduces the weight of the energy storage module and thereby increases the suitability of the energy storage module according to the invention for motor vehicles produced, for example, as lightweight constructions.
If no tie rod is provided for the bracing of the storage cells and the end plates, such a bracing can take place by a wrapping. A wrapping in the sense of the invention is a type of wrapping of the storage cell module with suitable materials which cause a stable connection between the storage cell stack and the end plates, so that the energy storage module will meet the necessary stability demands; i.e. it counteracts the deformation caused by pressure changes in the interior of the storage cell during the operation. Such wrappings may, for example, be implemented by means of metal strips, fiber materials or wires.
Conventional further components, such as electric connections and insulators between the cells and/or the storage cells and the bracing element, can complete the energy storage module according to the invention.
In an advantageous embodiment, it is provided that both end plates of the energy storage module have a layer structure of at least three layers. The weight reduction of the energy storage module according to the invention is thereby increased multiple times. The production expenditures and therefore the costs of the energy storage module according to the invention are thereby also reduced.
In a further preferred implementation, it is provided that the layer structure of the end plate is a sandwich-type structure, which comprises a first and a second outer layer and at least one inner layer, the first and second outer layer surrounding the inner layer and at least one outer layer or at least one inner layer consisting of a fiber composite material. As indicated above, fiber composite materials are known from the prior art. By using fiber composite materials in at least one layer of the at least three-layer end plate of the energy storage module according to the invention, while the stability of the end plate remains good or is even improved, the weight of the end plate and therefore that of the energy storage module according to the invention can be reduced because of the lower net weight of the fiber composite material. This is particularly advantageous if the energy storage module is provided for a vehicle of a lightweight construction.
Preferably, for example, the inner layer is formed of an injection-molding material containing fibers, and particularly of a thermoplastic material, the fibers preferably being short fibers which are homogeneously distributed in the injection-molding material. A homogeneous distribution of fibers in the sense of the invention is also a diffuse distribution, in which the fibers are arranged in all directions, thus anisotropically, however, the fiber density being essentially the same in all regions of the respective layer. In this case, the respective outer layers can be formed of conventional metals, such as aluminum. The layers are mutually connected in a conventional manner, as required, with the aid of fastening devices. The use of an inner layer made of the above-mentioned fiber composite material, while the stability is sufficient, significantly reduces the net weight of the end plate and thereby contributes to the weight reduction of the energy storage module according to the invention.
Furthermore, it is preferably provided that all layers, thus both outer layers and the inner layer as well as, if required, additional inner layers of the end plate of the energy storage module consist of a fiber composite material. This further reduces the weight of the energy storage module and, in addition, simplifies the production of the end plate because layers of fiber composite materials can be connected with one another particularly easily and well and without any high technical expenditures, whereby the stability of the end plate of the energy storage module according to the invention is clearly increased. This predominantly applies to identical fiber composite materials as well as to different fiber composite materials.
The end plate according to the invention preferably has a three-layer structure, in which the respective outer layers are formed by a fiber composite material, which has unidirectional long fibers in a preferably thermoplastic matrix material, the inner layer surrounded by the outer layers being formed by short fibers embedded in a preferably thermoplastic injection molding material. The presence of short fibers is not absolutely necessary but increases the stability of the inner layer by the diffuse arrangement of the short fibers. Furthermore, preferably all three layers have the same matrix material and, in particular, the same thermoplastic matrix material. This simplifies the production of the layer structure, thus the laminating of the layers, and results in a particularly good stability of the three-layer structure. In the case of different matrix materials, the different layers can be mutually connected, if necessary, with the aid of conventional fastening devices or adhesive materials. If the inner layer is formed of an injection molding material, this layer may also have an inherent structure and therefore does not have to have a planar design but can advantageously also have a type of wavy structure, which provides the end plate with additional stability with respect to deformation forces acting upon it.
In a further advantageous development, it is provided that the end plates as well as the tie rod consist of a fiber composite material. The fiber composite material of the end plates and of the tie rod may be the same material or different materials, preferably the same fiber composite material. As a result, the weight of the energy storage module is further efficiently reduced and its production is simplified because, as a result of the use of fiber composite materials for the tie rod as well as for the end plates, these can be easily mutually connected in a durable and efficient manner without any high technical expenditures. Furthermore, because of the use of the fiber composite material, as a rule, an electric insulation of the storage cells and of the seams of the storage cells and of the tie rod will not be necessary. This applies particularly when the fiber material also consists of an electrically non-conductive material.
According to another advantageous embodiment, the wrapping comprises an additional element, which at least partially surrounds the stacked storage cells as well as the end plates, and a fiber composite material, in which case the fiber composite material at least partially surrounds the additional element. As mentioned above, a wrapping is provided as an alternative to the use of a tension element or tie rod. In this embodiment, an additional element is placed around the cell module comprising stacked storage cells and end plate, which additional element surrounds the cell module at least partially. This additional element forms a stable base for the fiber composite material to be added later, so that the fiber composite material will not get between the stacked cells, and furthermore, a sufficiently stable bracing of the energy storage module according to the invention will be ensured. Suitable additional elements comprise, for example, possibly structured metal plates or metal sheets, which may also be constructed in several layers, duromeric or thermoplastic synthetic sections, such as duromeric honeycomb cores or thermoplastic deep-drawn sections. These additional elements may surround the cell module completely or only partially. This depends on the required stability and size of the energy storage module, thus, also on the pressure created in the interior of the storage cells during the operation of the energy storage module, and can take place in the suitable size and shape corresponding to the used material. In this case, a partial surrounding of the cell module by the additional element reduces the costs of the energy storage module. It is further provided that the additional element is at least partially surrounded by a fiber composite material. The latter may be wrapped or wound around the additional element and thereby also around the cell module in the form of a mat or a band and is provided with a matrix material which penetrates and/or surrounds the fiber structure, and thus contributes to the sufficient stability of the wrapping. The fiber material preferably is a roving or a fiber band made of several individual fibers which, before being wrapped around the additional element, is dipped into a bath containing the matrix material. If the matrix material is a thermosetting plastic, the energy storage module according to the invention is hardened after the completion of the wrapping whereby the thermosetting plastic obtains its final shape and stability, in which case, the hardening of the thermosetting plastic takes place by means of conventional methods, for example, by means of light curing or thermosetting. When a thermoplastic material is used, the latter is heated to its melting point or softening point, whereby it softens sufficiently and adheres to the fiber band (or roven) pulled through the bath. The hardening takes place by cooling the wrapped energy storage module.
As an alternative, the wrapping may also takes place such that an already pre-wrapped fiber structure provided with matrix material is stretched, for example, under the effect of heat and is put over the energy storage module or a provided additional element.
Advantageously, the fiber composite material for the end plate and/or the tie rod and/or the wrapping has a thermoplastic matrix with fibers or a duromeric matrix with fibers. Such fiber composite materials are easily available in the desired hardness or elasticity and are distinguished by low cost and, in addition, by insulating properties, whereby, as a rule, insulating layers between the individual storage cells as well as the storage cells and the tie rod will not be necessary, which clearly causes a simplification of the production and therefore also reduces the manufacturing costs. In addition, these materials have a low net weight in comparison to current extruded sections and are easily workable by means of conventional devices without any high technical expenditures, which keeps the production costs of the energy storage module according to the invention low. Particularly preferably, the fiber composite material is distinguished by a thermoplastic matrix with fibers, because, as a result of their melting capacity, thermoplastic materials can be worked particularly easily and nevertheless provide a sufficient stability. A thermoplastic that is particularly preferred because of the low cost and the good availability is polypropylene (PP).
According to a further advantageous embodiment, it is provided that the fibers of the composite material for the end plate and/or of the tie rod and/or of the wrapping are selected from glass fibers, carbon fibers, mineral fibers, such as basalt fibers, plant fibers, as, for example, cellulose fibers or hemp fibers, ceramic fibers, such as mullite fibers or SiC fibers, steel fibers or synthetic fibers, as, for example, polypropylene fibers, nylon fibers or aramid fibers or mixtures thereof. The fibers can be selected depending on the demand profile. Glass fibers are particularly preferred because they are characterized by high stability, good availability and electrically insulating properties. In addition, glass fibers can be obtained at reasonable cost in the necessary stability grades. This lowers the production costs of the energy storage module according to the invention while its stability is very good. The fibers may be present as long fibers or short fibers, long fibers clearly increasing the stability of the fiber composite material. Furthermore, the fibers may be unbound, thus be present as a disperse distribution in the matrix material. However, the fibers are at least joined to form fiber bundles or even fiber mats, weaves, knits, wovens, nonwovens and the like, because the stability of the fiber composite material is thereby increased multiple times.
The energy storage module according to the invention is further advantageously characterized in that the fibers are unidirectional fibers. This means that the fibers are present in the fiber composite material in a manner aligned in a preferred direction. This increases the stability of the fiber composite material precisely in this direction. For this reason, the fiber composite material, which has unidirectional fibers, is advantageously arranged in the loading direction, because the tensile strength of the fibers can thereby most efficiently counteract possible deformations as a result of the pressure change in the interior of the storage cells during their operation.
In a further advantageous embodiment, the end plates and/or tie rods of the energy storage module according to the invention have fastening elements and/or floor fastening elements. Fastening elements are used for connecting the end plates with the tie rod. Floor fastening elements are used for fastening an energy storage module, for example, with the surrounding housing of the energy storage module. Such fastening elements or floor fastening elements may, for example, be eyes, feet, ribs, lugs, notches, rivets or grooves. By means of, for example, corresponding lugs or eyes on an end plate as well as on a tie rod or tie rods between one another, for example, by means of the insertion of a pin or of a screw through both lugs, or eyes, a durable stable connection between the tie rod and the end plate can be provided in a simple manner. Such fastening elements are preferably an integral part of the component to be fastened (for example, the tie rod or the end plate), which is particularly made possible by the use of synthetic materials or fiber composite materials as the tie rod and/or the end plate. Integrated injection-molded-on fastening elements increase the connection with the surrounding components and thereby ensure sufficient stability of the energy storage module in its environment even under the influence of mechanical forces, as they are transmitted during the intended use of the energy storage module. The fastening element or floor fastening elements may be designed in any form, for example, as eyes, ribs, clips, lugs or bolts, and in any number. At least floor fastening elements are preferably provided at least on each floor-side corner of the energy storage module according to the invention. Fastening elements or floor fastening elements can easily be integrated in the corresponding component by means of current injection molding processes, whereby the production costs of the energy storage module and the technical expenditures for its production and thereby also its costs are considerably reduced. This is not least the result of the fact that possible finishing steps, such as the separate providing of fastening elements, are eliminated. Furthermore, the production of the energy storage module according to the invention can be more easily and more comprehensively automated, which prevents the occurrence of faults during the implementation and further also contributes to the lowering of production costs and to an increase in production.
According to a further advantageous embodiment, the end plates are mutually connected with the tie rod or several, thus more than two, tie rods by screwing and/or upsetting and/or welding and/or by means of at least one clip, and/or by means of a reshaping, in which case a tie rod reaches behind and/or reaches around, for example, an end plate. Suitable screwing devices are known from the state of the art. Wing screws have been very successful. In this case, the wing screw is guided through an eye provided, advantageously integrated, for example, in the end plate or in a first tie rod, as well as through an eye provided, advantageously integrated, in another tie rod, and screwed onto the end side by means of a wing nut, which clearly reduces the production-related expenditures, because a mounting of fastening elements is at least partially eliminated. Such a screwed connection ensures a permanent connection of the components. The tie rods may also have an upsetting deformation around at least a portion of the end plate or of a first tie rod, usually around at least a lateral edge, and be connected with it in this manner. In this case, upsetting deformations have the advantage of not requiring additional fastening elements. The upsetting deformation of a tie rod can comfortably take place after the arrangement of the cells, and be carried out individually, thus as a function of the size of the cell stack. In addition, tie rods can be welded to one another or also to end plates. Conceivable welding processes comprise ultrasonic welding, laser welding and friction welding. The suitable welding process is selected in coordination with the used materials. A welded connection ensures a permanent connection of the end plate with the tie rod or of the tie rods to be connected with one another. In a further development, the tie rods can be connected with one another or the tie rods can also be connected with the end plates by means of a clip. In this case, clip elements have the advantage that they can be mounted afterwards at any locations, thus after the arrangement of the cell stack, and therefore individually. Clip connections are independent of the size and shape of the cell stack, which reduces the production-related expenditures and permits a certain variability of the production process. If the tie rod as well as the end plate to be connected therewith comprises a thermoplastic material, the two components or also several tie rods among one another can be mutually connected also by heating the respective areas to be connected until the thermoplastic material has become soft and by a subsequent pressing against one another or pressing. The heating can, for example, be carried out, by means of mirror welding using a heatable aluminum plate. Such a plastic connection can be established in a simple manner and without any high technical expenditures and, after the hardening of the material, thus the cooling of the connected materials, provides a sufficiently stable connection of the components. Because of the reduced manufacturing expenditures, also as a result of the absence of separate or integrated fastening devices, the production costs and the technical and logistical expenditures of the production of the energy storage module according to the invention are reduced even more. This method is therefore particularly suitable for the production of cost-effective energy storage modules for motor vehicles of a lightweight construction. The respective fastening mechanisms may also be combined with one another, so that, for example, in addition to a welded connection, a screwed and/or bracing connection (clip connection) can be provided, which clearly increases the stability of the anchoring of the tie rods among one another or of the tie rods with the end plate.
Furthermore, a method is provided according to the invention for producing an energy storage module described above. The method comprises the providing of an end plate consisting of at least three layers and/or of a tie rod made of a fiber composite material, if required, the providing of fastening elements and/or floor fastening elements on at least one end plate and/or a tie rod, the mounting of at least one end plate respectively on the respective front face of the storage cells disposed at the end of the prismatic storage cells stacked in a row and the bracing of the end plates, preferably by way of at least one tie rod or a wrapping.
If the bracing of the end plates is carried out by means of a wrapping, advantageously the following process steps are carried out: Mounting of an additional element which at least partially surrounds the cell module of stacked storage cells and end plates; rotating of the cell module equipped with the additional element around a fiber band running through a resin bath and, if required, hardening of the energy storage module. A hardening step is provided particularly when duromeric materials are used and can take place by means of current processes, such as light hardening or thermosetting. If floor fastening elements, for example, are provided at the end plates, they will be left free during the wrapping, so that they can still carry out their function.
As an alternative to the above, the wrapping can also take place such that already shaped, thus wrapped fibers provided with a matrix material are stretched, for example, by heating and stretching the wrapping when thermoplastic matrix materials are used, and subsequently the wrapping is put over the cell module, where it then solidifies in its shape by cooling.
The advantageous embodiments described within the scope of the energy storage module according to the invention are correspondingly advantageously applied within the scope of the method according to the invention for producing the energy storage module.
A method of producing an energy storage module is thereby provided which is easy to implement and variable in its application. The method according to the invention requires only low production-related expenditures and thereby contributes to the lowering of the production costs of the energy storage module and thereby of its overall costs. By the providing of integrated fastening elements and/or integrated floor fastening elements, finishing steps are for the most part eliminated, which again reduces the costs for the production of the energy storage module according to the invention. In addition to a high quality, a mechanical, chemical and physical stability and an efficient operating mode, the energy storage module according to the invention has a lower net weight than energy storage modules comprising extruded sections, whereby the total weight of a motor vehicle containing the energy storage module according to the invention is reduced, so that it is particularly suitable for motor vehicle of a lightweight construction. Because of the reduced production costs, the costs of the energy storage module are also low.
In the following, the invention will be explained in detail by means of the drawing.